This invention relates generally to apparatus for mixing and dispensing granular materials and is particularly directed to portable apparatus for mixing, wetting and discharging pre-blended granular materials, such as cementitious-type materials, at a remote construction site.
The products to which this invention applies can vary from concrete mixes, including bricklaying mortars and grouts. The traditional method of producing mortar or grout at a masonry job site is to count shovelfuls from a pile of sand, add mortar/cement by breaking open a 90 lb. paper bag, followed by adding water with a pail to a batch mixer. This method is still used on 80% of masonry construction jobs. Basic drawbacks of this approach are that it is labor-intensive and that the mix composition varies depending on type or condition of the sand, which when damp can increase the mixture volume by as much as 30%. Since sand is the predominant ingredient, variation in the mixture composition is inherent in the method of counting shovelfuls and cannot be precisely controlled. Mortar bond-strength, compressive strength, color and other factors of the mortar also vary. This can cause many serious problems that sometimes lead to removal of defective material, which, of course, is usually very costly.
Another method of producing mortar that addresses some of the aforementioned problems is to dry sand at a remote location and pre-blend the components, i.e., sand, mortar cement, lime and even color additives, and package the blend in bulk bags (2000 to 4000 lb.) and deliver the bags to a job site. In one approach, the bulk bags are individually placed in a silo that contains up to six bags of material. The contents of the silo is then dispensed into a batch-type mixer wherein water is added. This approach can be used to produce both grout and mortar, but requires at least two silos and two batch mixers (one for each type of material). The silo is portable only when empty to facilitate set-up delivery to a job-site. At the job site, it is set up as a fixed mixing operation remotely located from where the masonry brick laying operation is taking place. The mixing cycle is also labor intensive, requiring two workers, a forklift operator and a laborer to supply the masonry laying crew with mortar or grout.
This silo mixing operation begins with the forklift operator exchanging a full tub with an empty tub which the mixed contents are later emptied into. A laborer using a bucket pours half of the needed water into the empty batch mixer and opens a slide gate, where by gravity alone dry pre-blended mortar empties into the batch mixer below. The quantity of dry material cannot be accurately measured because opening and closing of the slide gate doesn""t always cause the material to flow. The material bridges and does not flow easily. The laborer then uses a shovel to bang on the steel silo with the slide gate open which often results in the discharge of too much material. When this happens the equipment (mixer) is strained, can break down and material is wasted. This labor intensive mixing cycle continues with more water added as needed. Specifications require a minimum of five minutes mixing time. If the mix is too wet, more dry materials must be added resulting in opening and closing of the slide gate.
Another problem with this approach is in the variation in size between the various grades of sand and cement particles which promotes segregation because the material is handled and dispensed numerous times. One reason for this is that as the material flows into a silo, the material beneath the inlet of the silo piles up at the so-called xe2x80x9cangle of responsexe2x80x9d of the material. In this case, the larger particles often roll down the peak towards the sides of the silo, leaving the finer particles in the central region. Inhomogeneity can also occur when the silo is filled and the material is drawn off through an outlet at the bottom of the silo or bulk bag. The material flows from the region directly above the opening and thus is not representative of the material in the originally packed bulk bag. To avoid this problem, the pre-blended suppliers use too fine a sand that meets only the minimum sand grading specifications as described in ASTM C144 xe2x80x9cSpecifications for Aggregates for Masonry Mortarxe2x80x9d. A better product has a larger variation in sand gradation.
In addition to the problem of inconsistent mixture composition control, the silo approach also suffers from an unhealthy work environment because of the very dry sand falling on the laborer. Opening and closing of the overhead slide gate showers the laborer with very dry cementitious blended materials. The laborer ingests these sand and cement particles in the air he breathes which can cause silicosis and possibly cancer. This batch mixing operation cannot be made dust proof. The laborer""s clothes are covered with dust which is brought home to possibly contaminate others. A batch mixer having a gasoline engine also endures further abuse by the intake of dust parties which can cause premature machine wear and necessitates more frequent replacement of air filters.
The mixing cycle continues and additional labor costs add up. The mixed contents are emptied into the mortar tub. The forklift operator now must stop other operations to exchange the full tub with an empty one, then carry the tub to the scaffold that may be hundreds of feet away from the mixing operation. This silo mixing operation is thus not portable, but rather is fixed in location. The 20,000 lb. weight of the forklift constantly traveling over dirt creates dust that slows the work. Another laborer at the top of the scaffold typically removes safety railings to allow the full tub to be placed on the scaffold. The forklift then moves over to pick up and lower an empty tub. The safety railings must then be reinstalled. The operation is not finished! The mortar must now be spread to the individual bricklayers by shoveling from the tub to the mortar boards so that the mortar is within easy reach of the individual bricklayers.
If the material is grout, labor costs to fill block is even a bigger factor because grout must be placed in buckets, then passed hand to hand, and poured into each individual block core by the bricklayers. This is wasteful because in addition to the time required to perform the needed operation, the bricklaying must stop in order to grout the block walls. In an attempt to address the high costs of this operation, a powered grout dispenser has been developed that must be filled at the mixing stage with all the accompanying labor intensive operations described for mixing mortar. This operation usually starts by elevating the batch mixer under the silo, charging the batch mixer with grout material, adding water and mixing for five minutes, then dumping the contents into the grout hopper. The wet mixture must then be transported to the work area where grout is dispensed from the holding hopper and directed to the block cores. The alternative to this is to fill the hopper with pre-mixed grout from a ready-mix cement truck, but this suffers from the problems of delivery truck availability and scheduling and additional costs.
Another type of mixing operation can be performed by a silo system using dry pre-blended material delivered to the job site by a bulk delivery truck that blows the material directly into the silo. The mixing can be performed by a continuous mixer installed under the silo. This approach is common in Europe and marketed as PFT, WAM. The mixed material is then typically pumped by a grout pump up to 200 ft. away where it is dispensed. The drawback in this approach is that additional equipment is required (pump and hoses), which must be cleaned and maintained. While this approach has been used in Europe for twenty years, it is not practical for masons in the United States who generally are capable of much higher levels of productivity and are less adapted for maintaining complicated machinery.
The various approaches discussed above each address specific problems encountered in the prior art, but also suffer from various limitations. There is currently no single mortar-blend delivery apparatus or method which combines the most advantageous features discussed above and allows for simple, efficient delivery of pre-mixed dry mortar-blended products. The present invention solves the problems and shortcomings of the prior art discussed above as described in the following paragraphs.
Accordingly, it is an object of the present invention to provide improved apparatus for mixing and delivering pre-blended granular mixtures onsite where the granular mixtures are to be used.
It is another object of the present invention to reduce the costs of mixing and dispensing cementitious compositions such as used by bricklayers at construction job sites.
A further object of the present invention is to mix at a job site pre-blended cementitious-based granular mixture with water to form a viscous solid-liquid suspension for use in masonry work in building construction.
Still another object of the present invention is to provide portable apparatus for mixing and dispensing pre-blended cementitious granular mixtures such as mortar and grout which can be easily moved to and positioned at the site of use.
A still further object of the present invention is to provide an environmentally clean, cost saving mixing and delivery apparatus for pre-blended granular mixtures which affords precise control of the proportions of the granular mixture components, requires fewer workers to operate, and is lightweight and compact to permit it to be easily positioned immediately adjacent to where the mixture is to be used.
The present invention contemplates a portable mixing/delivery apparatus for pre-blended granular mixtures which is user friendly, saves labor and delivers a quality mix. The inventive mixing/delivery apparatus takes the guess work out of the mixing process that heretofore allowed too much variation in mortar consistency. The inventive mixing/delivery apparatus is dust-proof, can be turned on or off as needed, and is adjustable in height for supporting a bulk bag of pre-blended materials. The bulk bag can be placed on top of the apparatus"" steel framework by a forklift using a removable top frame and is safely held in place by the weight of the bulk bag. The discharge spout of the bulk bag empties into a receiving cylinder section that forms the intake of a hopper for receiving the dry pre-blended materials. The contents of the bag discharge into the dry end of a continuous mixer having a dynamic input mixing stage, an output dry-to-wet mixing stage, and a transition stage therebetween. An auger mixes the dry mortar that can segregate as it freely flows under gravity to the input stage and a horizontal metering screw moves the material forward in the continuous mixer. The metering screw extends into the tube-like transition stage. The entire assembly (bulk bag, support frame and continuous mixer) is portable and can be lifted to the desired height of a masonry scaffold by a forklift. Auxiliary hydraulic controls of the forklift with suitable hydraulic quick connects power the hydraulic motor of the continuous mixer. The inventive mixing/delivery apparatus allows the continuous mixer discharge tube end to rotate (90xc2x0 either left or right) to facilitate material dispensing to either a mortar tub, or directly to mortar boards. Grout material can be poured directly into the hollow cores of cement blocks by extending the discharge tube with a flexible hose attached to the end of the tube. When the desired quantity is mixed, the apparatus is turned off, lowered and set on the ground, or moved where it can be reused at other work areas. The entire apparatus with optional gasoline, electric or hydraulic motor and controls can be set up on a heavy duty scaffold where it can be used as needed without lowering to the ground. A source of water is connected to the continuous mixer""s mixing tube for forming a wetted mortar slurry. The auger and mixing tube combination is detachably connected to facilitate dismantling and clean up. A pair of closure plates are disposed adjacent to the aperture in the hopper for adjusting or shutting off the flow of mortar from the hopper to the transition tube.